Cruise control systems are employed extensively in modern automobiles. Conventional cruise control systems regulate vehicle speed to a an operator set speed in accordance with well known PID speed controllers. Adaptive cruise control systems are also known wherein the following distance of an adaptive cruise vehicle relative to a preceding vehicle is controlled. The following distance may be a set distance or a variable distance as a function of vehicle speed. Vehicle separation may be determined, for example, by radar, infrared, ultrasonic or other means.
Speed control or following distance of such conventional or adaptive cruise control equipped vehicles ultimately depends upon the control of drive torque produced by the vehicle. In internal combustion engines, torque is generally a function of the air ingested by the cylinders (intake air) among other factors. Intake air is controlled by throttling an air passage upstream of the cylinders.
Vehicular power take-off (PTO) systems are known which provide for a mechanical output from an internal combustion engine or portion of the vehicle drivetrain to drive accessory loads such as electrical generators or mechanical or hydraulic apparatus. PTO is operator invoked generally in accordance with a selected engine speed setting. Speed control of the engine ultimately depends upon the engine torque required to provide the needed PTO torque requirements at the selected set speed. As previously stated torque is generally a function of intake air ingested by the internal combustion engine. And, intake air is controlled by throttling.
Mechanically linked throttle systems are known wherein intake air is throttled in substantial accordance with the throttle pedal position under control of the vehicle operator. Such mechanically linked systems similarly employ mechanically linked throttle actuators to establish position authority over the throttle valve for cruise control and PTO applications—typically by a valve controlled vacuum actuator and cabled arrangement. Electronic throttle control systems are known which mechanically decouple the throttle valve from the throttle pedal. Such systems generally employ throttle pedal position sensing and stepper motor actuation of a throttle valve. Throttle valve position sensing is also generally employed in both mechanically linked and electronically controlled throttle systems.
Throttle authority is conventionally set to an upper limit of substantially 100% (fully open) when a cruise control or PTO system is activated. It is generally desirable to provide for broad throttle authority during cruise control since vehicle throttle requirements can vary substantially with load, grade and altitude. It is known in cruise systems, for reasons including driveability considerations, to provide a throttle limit during resume and acceleration cruise operations. Such limits are known to be substantially fixed throttle position settings and may be a setting substantially in excess of a current throttle position.
Such broad limits on throttle authority may in the event of certain control corruption necessitate operator intervention in order to manage the throttle as desired to maintain the operator's objective of vehicle speed or following distance in a cruise control mode or engine speed in a PTO mode. Generally, however, it is desirable to minimize the amount of operator interaction that is required, even in the event of a control corruption. Therefore, a need exists to limit the required operator intervention required in the event of control corruption while at the same time not unnecessarily limiting throttle authority.